1. Field of the Invention
The present invention relates to insulated ultrafine powder, a process for producing the same and a resin composite material which makes use of the same and features a high dielectric constant. This material is well suited to the formation of an IC (integrated circuit) package, a module substrate and an electronic part integrated with a high dielectric constant layer. In particular, the material is well suited to the formation of an inner layer capacitor layer of a multi-layer system wiring substrate. In addition, the material is useful for miniaturizing built-in antenna for wireless LAN and RFID (Radio Frequency Identification) and also thinning electromagnetic absorption sheets, units and panels which prevent electric wave interference inside a high frequency electronic machinery and equipment.
2. Description of the Related Arts
As one of the causes for data errors of an IC, there exists influence due to a high frequency noise. There is known a method for removing a high frequency noise by equipping a wiring substrate with a capacitor having a large capacity, which is materialized by forming a high dielectric constant layer on a wiring substrate. With regard to miniaturization of built-in antenna for wireless LAN and RFID (Radio Frequency Identification) and thinning of electromagnetic absorption sheets, units and panels, the sizes thereof are each in nearly inverse proportion to the square root of the dielectric constant and accordingly, a high dielectric constant material is useful for miniaturization and thinning of these members. In particular, it is required to impart the above-mentioned characteristics to a resin material excellent in processability and moldability.
There is proposed as a prior art, a resin composite material incorporated with at least 65 vol % of a ferro-electric material typified by barium titanate as a high dielectric constant filler (refer to Japanese Patent Application Laid-Open No. 237507/20001). The reason for necessity of a large amount addition of such strongly dielectric filler is described hereunder. In the case of a small amount of the filler being added, a high dielectric constant filler is made into a state of being insulated to a resin having a relative dielectric constant of about 3. When this state is taken into consideration by means of an equivalent circuit, it is represented by a series circuit including a low capacitance corresponding to a low dielectric constant resin and a high capacitance corresponding to a high dielectric constant filler. Since in this case, the reciprocals of the dielectric constant have additive properties, even when the high dielectric constant filler is added at a rate of, for instance, 50 vol %, the dielectric constant of the resin composite material is made to be as low as about 6. In order to avoid such inconvenience, the equivalent circuit of the composite material needs to be a parallel circuit. Thus as a preferable embodiment, it is necessary to form a continuous layer of the high dielectric constant filler inside the composite material.
In order to form such a continuous layer and thus contrive high dielectric constant of the composite material, it has been made necessary to add at least 65 vol % of a high dielectric constant filler as a ferro-electric material. Such being the case, for the purpose of realizing a relative dielectric constant of at least 20, it is made necessary to add at least 80 wt % (50 vol %) of a high dielectric constant filler as a ferro-electric material, whereby the processability and moldability that are the characteristics inherent in a resin material are unfavorably impaired in compensation for the achievement of a high dielectric constant. No countermeasure has heretofore been taken at all in any of the prior arts regarding the essential cause for a large amount of a filler to be added.